Field of the Invention
The present invention relates generally to a knee resurfacing prosthesis and more specifically it relates to a knee implant prosthesis for knee resurfacing.
Description of the Related Art
It can be appreciated that knee-resurfacing prostheses have been in use for years to treat articulating surfaces destroyed by arthritis or pathological processes secondary to trauma. Basically, the natural knee joint comprises an upper femoral articulating surface having two condylar surfaces and a lower tibial plateau comprising two cupule shaped tibial condyles articulating smoothly with the upper femoral condyles. Typically, knee replacement prostheses are comprised of several types of prostheses, where articulating components of the knee are removed and replaced with metal and polyethylene components.
Prior art devices have attempted to duplicate the geometry of the natural articulating surface, where the femoral component has a semicircular C shaped design such as depicted in a U.S. Pat. No. 4,224,696. The bicondylar design is similarly disclosed in prior patents by F. Buechel and Pappas in U.S. Pat. Nos. 4,309,778 and 4,470,158. A more recent bicondylar design is described in U.S. Pat. No. D473,3075 and U.S. Pat. No. 6,197,064 B1. The prior art describes the bicondylar prosthesis as having a middle patellar groove for the femoral patellar articulation. Other knee implant devices are used to resurface only one femoral condyle such as unicondylar prostheses described in U.S. Pat. No. 7,141,053 and U.S. Pat. No. 6,726,724. Multiple designs of hinged implants also have been described basically for use in revision procedures and cases where bone loss and instability precluded the use of conventional implants. The design of the present invention is not a hinge. And, unlike hinged designs, my design allows the two articulating surfaces of the tibia and the femur to separate slightly in extreme ranges of motion such as squatting or during running.
In these respects, the reverse knee resurfacing prosthesis according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of resurfacing the articulating surfaces of the femur and the tibia using a reverse geometry where the femoral component has the shape of a cupule and the preferred embodiment of the tibial component has the shape of a trochlea, a cylinder or curved surface having a groove it its middle portion. In doing so, the reversed geometry provides significant advantages, both mechanical and anatomical, over previously known knee implants. The mechanical advantage being a significant increase in the contact surface between the tibia and the femur thereby reducing pressure forces and consequently reducing wear.
In previously known implants, the curved femoral implant surface contacts the flat tibial articulating surface with a very small surface area and, as a result, the pressure load can exceed three to four times the body weight. This stress concentration increases wear of the polyethylene tibial tray and reduces the efficacy and life of the implant. In my reverse knee implant, the contact surface encompasses the concave surface of the femoral cup, thereby distributing the pressure load over a large surface and minimizing wear. The anatomical advantage lies in the fact that my reverse geometry and anterior lip feature eliminates the need for cruciate ligaments. The shape of my femoral cup provides considerable stability in the anterior-posterior plane and prevents the femur from sliding forward. During the stance and swing phase of ambulation, the constraining geometry of the anterior and posterior lips of the femoral cup replace the mechanical effect of the anterior and posterior cruciate ligaments.